US 2014/0226158 A1 discloses systems and methods which analyze light to determine the size and characteristics of particles. The described systems and methods are complicated and expensive.
U.S. Pat. No. 4,871,251 discloses an apparatus for analyzing particles contained in a fluent medium. The apparatus includes a body having a window, an optical source preferably comprising a laser diode having a small light emitting area, and an optical system for focusing the light from the laser diode at a focal spot such that the size of the focal spot is approximately equal to the size of the light emitting area of the laser diode. A photodetector is mounted in the body and detects light backscattered from the focal spot by particles in the fluent medium, and produces an electrical signal that comprises a series of pulses associated with the particles. The electrical signal is input to a detector that counts the pulses and indicates the number of particles in the fluent medium.